The present invention relates to eyeglasses, and more particularly to optical measuring devices and methods for checking certain measurements taken of a patient's face before these measurements are used to create eyeglass lenses for the patient.
Progressive addition lenses (sometimes called no-line bifocals) are used for patients who need to see clearly both near and far. Such lenses include a clear channel through which the patient looks. It is important that such lenses, or any prescription lenses, be correctly mounted and properly positioned in the frames to fit the patient correctly for clear comfortable vision. In particular, prescription lenses need to be mounted in their frames so that they are properly positioned relative to the pupils of the patient when the patient wears them.
In order for a patient to be satisfied with their prescription lenses, it is important that accurate measurements of the patient's face be taken and verified before the lenses are created and mounted in the frames. The critical measurements include (a) the monocular pupillary distance for each eye (right/left), which is the distance from the center of the nose to the center of the pupil; and (b) the segment (seg) height for each eye (right/left), which is the distance from the bottom of the frame where the lens sits to the center of the pupil. In most cases, it is also important to know the thickness of the frame itself. Although devices exist for taking these measurements, the measurements taken may be imperfect or imprecise, or errors may occur, which may result in the creation of lenses that are unsuitable for the patient. When this occurs, the lenses must be remade, resulting in additional cost to the eye doctor, lab and/or patient.
Before new lenses are ordered, the monocular pupillary distance and the segment height for each eye of the patient are measured. The thickness of the particular frame in which the lenses are to be mounted is also determined. This information is then used to create a set of lenses for the patient to be mounted in the particular frame. Unfortunately, the measurements taken may or may not be accurate, depending on the method used. In some cases, no double checking is done, resulting in unverified measurements being sent to the lab with instructions to create lenses. This could result in the creation of unsuitable lenses, in which case the lenses would have to be discarded and redone, resulting in losses and delays.
One current method for checking the monocular pupillary distance and the segment height measurements of the patient involves the use of a centration chart. This is a flat sheet having measurement lines thereon. A set of demo lenses are inserted into the eyeglass frame selected by the patient, and placed on this chart for visual inspection. The chart provides a very rough and imprecise check of the measurements taken, and may not detect positioning errors of up to 2 mm, which is more than enough for a patient to be dissatisfied with the result.
It is therefore desirable to be able to precisely check the measurements of a patient's right and left monocular pupillary distance and segment height before they are sent to a lab for creation of lenses, particularly progressive addition lenses, so that suitable lenses are created for the patient.
The present invention provides methods and apparatus for quickly and precisely performing such checking.